Cathode hybrid electrolyte for solid secondary battery, cathode including the cathode hybrid electrolyte, method of preparing the cathode, and solid secondary battery including the cathode hybrid electrolyte

ABSTRACT

Provided are a cathode hybrid electrolyte for a solid secondary battery, a cathode including the cathode hybrid electrolyte, a method of preparing the cathode, and a solid secondary battery including the cathode hybrid electrolyte, wherein the cathode hybrid electrolyte includes an ion conductor represented by Formula 1, and an ionic liquid, where at least a portion of the anions of the ionic liquid comprise the same anionic moiety —Y −  of the ion conductor, 
     
       
         
         
             
             
         
       
     
     where, in Formula 1, X, R 1  to R 3 , Y − , and n are the same as defined in the detailed description.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2019-0138197, filed on Oct. 31, 2019, in the KoreanIntellectual Property Office, and all the benefits accruing therefromunder 35 U.S.C. § 119, the content of which is incorporated herein inits entirety by reference.

BACKGROUND 1. Field

The present disclosure relates to a cathode hybrid electrolyte for solidsecondary batteries, a cathode including the cathode hybrid electrolyte,a method of preparing the cathode, and a solid secondary batteryincluding the cathode hybrid electrolyte.

2. Description of Related Art

Recently, in accordance with industrial requirements, development ofbatteries with high energy density that are safer has becomeincreasingly important. For example, lithium-ion batteries have been putto practical use in the automotive field as well as ininformation-related equipment and communication equipment. In the fieldof automobiles, safety is particularly important because it affects aperson's life.

Currently available lithium ion batteries use an electrolytic solutionincluding a flammable organic solvent, which results in the possibilityof overheating and fire when a short circuit occurs. In contrast, asolid battery using a solid electrolyte instead of an electrolyticsolution has been proposed.

In a solid battery, the possibility of a fire or an explosion, even whena short circuit occurs, may be greatly reduced by not using a flammableorganic solvent. Therefore, a solid battery has a possibility of beingsafer compared to a lithium-ion battery using an electrolyte.

As a cathode active material of a solid battery, a cathode activematerial having stability at high voltage is used. However, when thecathode active material is excellent in high voltage stability, thewettability of the ionic liquid impregnated in the cathode is needed, inorder to reduce the interfacial resistance between the cathode and thesolid electrolyte of the solid secondary battery.

SUMMARY

Provided are cathode hybrid electrolytes for solid secondary batteries,the cathode hybrid electrolytes being solidified to prevent leakage tothe outside and having improved wettability with respect to cathodes.

Provided are cathodes including the cathode hybrid electrolytes andmethods of preparing the cathode hybrid electrolytes.

Provided are solid secondary batteries having improved cell performanceby including cathodes including the cathode hybrid electrolytes.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments of the disclosure.

According to an aspect of an embodiment, a cathode hybrid electrolytefor a solid secondary battery includes an ion conductor represented byFormula 1 and an ionic liquid, wherein an anion of the ion conductorincludes the same moiety of an anion of the ionic liquid.

In Formula 1,

X is an unsubstituted or substituted C6-C30 arylene group, anunsubstituted or substituted C2-C30 heteroarylene group, or —C(═O)O—R₇—,

R₇ is an unsubstituted or substituted C1-C30 alkylene group or anunsubstituted or substituted C6-C30 arylene group,

R₁ to R₃ are each independently hydrogen, an unsubstituted orsubstituted C1-C20 alkyl group, an unsubstituted or substituted C6-C20aryl group, or an unsubstituted or substituted C2-C30 heteroaryl group,

—Y⁻ is an anionic moiety, and

n is the degree of polymerization, which is a number in a range of 10 to500.

According to an aspect of another embodiment, a cathode for a solidsecondary battery includes a cathode active material; and the cathodehybrid electrolyte.

According to an aspect of another embodiment, a solid secondary batteryincludes a cathode; an anode; and a solid electrolyte disposed betweenthe cathode and the anode, wherein at least one of the cathode or theanode includes the cathode hybrid electrolyte.

According to an aspect of another embodiment, a method of manufacture ofa cathode for a solid secondary battery includes preparing a cathode byforming a cathode active material layer including a cathode activematerial on a cathode current collector; providing a hybrid electrolytecomposition including a monomer represented by Formula 20 and an ionicliquid to the cathode; and applying light or heat to the provided hybridelectrolyte composition to cause a polymerization reaction, to obtain acathode for a solid secondary battery including a cathode activematerial; and the cathode hybrid electrolyte.

In Formula 20,

X is an unsubstituted or substituted C6-C30 arylene group, anunsubstituted or substituted C2-C30 heteroarylene group, or —C(═O)O—R₇—,

R₇ is an unsubstituted or substituted C1-C30 alkylene group or anunsubstituted or substituted C6-C30 arylene group,

R₁ to R₃ are each independently hydrogen, an unsubstituted orsubstituted C1-C20 alkyl group, an unsubstituted or substituted C6-C20aryl group, or an unsubstituted or substituted C2-C30 heteroaryl group,and

—Y⁻ is an anionic moiety, wherein an anion of the ionic liquid comprisesthe same anionic moiety —Y⁻ as in Formula 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic view of a structure in which a cathode including ahybrid electrolyte is disposed on a solid electrolyte, according to anembodiment;

FIG. 2 shows the result of a linear sweep voltammetry (LSV) analysisperformed on a hybrid electrolyte of Example 1;

FIG. 3 shows a voltage change according to a capacity per unit area ofeach of solid secondary batteries according to Examples 5 and 6 andComparative Examples 4 and 5;

FIG. 4 shows a capacity change according to a number of cycles regardingsolid secondary batteries prepared in Example 5 and Comparative Example5; and

FIG. 5 is a cross-sectional view of a solid secondary battery accordingto an exemplary embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. Expressionssuch as “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist.

Hereinafter, a cathode hybrid electrolyte for a solid secondary battery,according to an embodiment; a cathode including the cathode hybridelectrolyte; a method of preparing the cathode; and a solid secondarybattery including the cathode hybrid electrolyte will be described indetail.

According to an aspect of an embodiment, provided is a cathode hybridelectrolyte for a solid secondary battery, the cathode hybridelectrolyte including an ion conductor represented by Formula 1 and anionic liquid, wherein an anion of the ion conductor includes the samemoiety with an anion of the ionic liquid.

In Formula 1,

X is an unsubstituted or substituted C6-C30 arylene group, anunsubstituted or substituted C2-C30 heteroarylene group, or —C(═O)O—R₇—,

R₇ is an unsubstituted or substituted C1-C30 alkylene group or anunsubstituted or substituted C6-C30 arylene group,

R₁ to R₃ are each independently hydrogen, an unsubstituted orsubstituted C1-C20 alkyl group, an unsubstituted or substituted C6-C20aryl group, or an unsubstituted or substituted C2-C30 heteroaryl group,

—Y⁻ is an anionic moiety, and

n is the degree of polymerization, which is a number in a range of 10 to500, for example, a number in a range of 20 to 400, for example, anumber in a range of 30 to 300, for example, a number in a range of 50to 200.

The cathode hybrid electrolyte may further include a lithium saltdifferent from the ion conductor of Formula 1.

In Formula 1, R₁ to R₃ may be, for example, hydrogen, a methyl group, anethyl group, a propyl group, an isopropyl group, a pentyl group, or abutyl group. Also, R₇ may be, for example, a methylene group, anethylene group, a propylene group, a pentylene group, or a hexylenegroup.

In the solid secondary battery, it is common to impregnate a cathode ina mixture including an ionic liquid to improve interface characteristicsbetween the cathode and a solid electrolyte and a conductivity of thecathode. However, when a cathode active material including a cathodeactive material having excellent stability with respect to a highvoltage such as a lithium cobalt oxide (LiCoO₂) is used in preparationof a cathode, the wettability of the cathode active material withrespect to the cathode is insufficient due to a high viscosity of amixture including an ionic liquid, and the mixture including the ionicliquid may leak to the outside as the charge-discharge cycles arerepeated.

In this regard, to resolve this problem, the present inventors haveinvented a cathode hybrid electrolyte for a solid secondary battery, ofwhich leakage to the outside is prevented and the wettability of theelectrolyte with respect to a cathode improves by reducing a viscosityof the electrolyte.

The cathode hybrid electrolyte according to an embodiment includes anion conductor represented by Formula 1 and an ionic liquid, wherein ananion of the ion conductor of Formula 1 has the same moiety of an anionof the ionic liquid. Thus, unlike a conventional mixture including anionic liquid, the cathode hybrid electrolyte has a solidified form, andhas a wettability with respect to a cathode that is improved due to areduced viscosity, and has an improved miscibility as compared with amixture including an ionic liquid. Therefore, when the hybridelectrolyte is used, not only leakage of the hybrid electrolyte to theoutside may be suppressed despite repeated charge-discharge cycles, butalso a lithium ion mobility in the cathode may effectively improve.

FIG. 1 shows a structure including a cathode impregnated with a cathodehybrid electrolyte and a solid electrolyte, according to an embodiment.

A cathode 13 has a cathode active material layer 11 and a cathode hybridelectrolyte 10 that are stacked on a solid electrolyte 12. As shown inFIG. 1, the cathode 13 is impregnated with the cathode hybridelectrolyte 10, which is particularly disposed in a solidified statearound the cathode active material layer 11. In this regard, unlike aconventional mixture including an ionic liquid, a current collector maynot be contaminated since the solidified cathode hybrid electrolyte 10does not leak to the outside, and thus a side reaction between thecathode hybrid electrolyte 10 and the solid electrolyte 12 may besuppressed. Although not shown in FIG. 1, the cathode hybrid electrolyte10 may exist in an interface between the cathode active material layer11 and the solid electrolyte 12.

Also, when the cathode hybrid electrolyte is included in the cathode, aninterface resistance between the cathode and the solid electrolyte maydecrease, and a lithium ion mobility in the cathode may increase.

The cathode hybrid electrolyte 10 according to an embodiment may includean ion conductor represented by Formula 1, and thus a lithium ionmobility may improve. The ion conductor of Formula 1 can serve as asingle lithium ion conductor due to its structural characteristics.

In Formula 1, —Y⁻ Li⁺ may be, for example, a group represented byFormula 2 or Formula 3.

In Formula 2, Rf may be a fluorine atom, an unsubstituted or substitutedC1-C30 fluorinated alkyl group, an unsubstituted or substituted C6-C30arylene group, or a combination thereof.

In Formula 2, Rf may be, for example, CF₃, F, or CF₂CF₃.

The ion conductor represented by Formula 1 may be, for example, acompound represented by Formula 4 or a compound represented by Formula5.

In Formula 4, n may be a number in a range of 10 to 500; R₁ to R₃ may beeach independently hydrogen or a C1-C20 alkyl group; and Rf may be afluorine atom, an unsubstituted or substituted C1-C30 fluorinated alkylgroup, an unsubstituted or substituted C6-C30 arylene group, or acombination thereof.

In Formula 5, n may be a number in a range of 10 to 500; R₁ to R₃ may beeach independently hydrogen or a C1-C20 alkyl group; and Rf may be afluorine atom, an unsubstituted or substituted C1-C30 fluorinated alkylgroup, an unsubstituted or substituted C6-C30 arylene group, or acombination thereof.

In Formulae 4 and 5, n may be, for example, a number in a range of 20 to400, for example, a number in a range of 30 to 300, or, for example, anumber in a range of 50 to 200.

The ion conductor represented by Formula 1 may be, for example, acompound represented by Formula 6, Formula 6-1, Formula 6-2, Formula 7,Formula 7-1, or Formula 7-2, or a combination thereof.

In Formulae 6, 6-1, and 6-2, n may be a number in a range of 10 to 500,Formula 7 Formula 7-1 Formula 7-2

In Formulae 7, 7-1, and 7-2, n may be a number in a range of 10 to 500.

In Formulae 6, 6-1, 6-2, 7, 7-1, and 7-2, n may be, for example, anumber in a range of 20 to 400, for example, a number in a range of 30to 300, or, for example, a number in a range of 50 to 200.

The hybrid electrolyte may further include a lithium salt different fromthe ion conductor of Formula 1.

An amount of the ion conductor may be in a range of about 0.1 parts toabout 50 parts by weight based on 100 parts by weight of the lithiumsalt. When the amount of the ion conductor is within this range, theresulting lithium ion mobility in the cathode may be excellent.

An amount of the ionic liquid in the cathode hybrid electrolyte may bein a range of about 1 part by weight to about 50 parts by weight, about1 part by weight to about 40 parts by weight, about 5 parts by weight toabout 30 parts by weight, about 10 parts by weight to about 30 parts byweight, or about 10 parts by weight to about 20 parts by weight, basedon 100 parts by weight of the lithium salt. When the amount of the ionicliquid is within these ranges, the interfacial resistance between thecathode and the solid electrolyte may decrease, and the conductivity ofthe cathode may improve.

The ionic liquid may be a compound represented by Formula 8, a compoundrepresented by Formula 9, or a combination thereof.

In Formula 8, X₁ may be —N(R₂)(R₃)(R₄) or —P(R₂)(R₃)(R₄); and

R₁, R₂, R₃, and R₄ may be each independently an unsubstituted orsubstituted C1-C30 alkyl group, an unsubstituted or substituted C1-C30alkoxy group, an unsubstituted or substituted C6-C30 aryl group, anunsubstituted or substituted C6-C30 aryloxy group, an unsubstituted orsubstituted C2-C30 heteroaryl group, an unsubstituted or substitutedC2-C30 heteroaryloxy group, an unsubstituted or substituted C4-C30cycloalkyl group, an unsubstituted or substituted C3-C30heterocycloalkyl group, or an unsubstituted or substituted C2-C100alkylene oxide group.

In Formula 9,

may be a heterocycloalkyl ring or a heteroaryl ring including 1 to 3heteroatoms and 2 to 30 carbon atoms, wherein the ring is substitutedwith a substituent or unsubstituted; X₂ is —N(R₅)(R₆), —N(R₅), —P(R₅),or —P(R₅)(R₆); and the substituent in the ring, R₅, and R₆ are eachindependently hydrogen, an unsubstituted or substituted C1-C30 alkylgroup, an unsubstituted or substituted C1-C30 alkoxy group, anunsubstituted or substituted C6-C30 aryl group, an unsubstituted orsubstituted C6-C30 aryloxy group, an unsubstituted or substituted C2-C30heteroaryl group, an unsubstituted or substituted C2-C30 heteroaryloxygroup, an unsubstituted or substituted C4-C30 cycloalkyl group, anunsubstituted or substituted C3-C30 heterocycloalkyl group, or anunsubstituted or substituted C2-C100 alkylene oxide group; and

Y⁻ may be an anion.

In some embodiments at least a portion of the anions Y⁻ of the ionicliquid represented by Formula 8 may include the anionic moiety —Y⁻ asdescribed in Formula 1. In some embodiments, all or substantially all ofthe anions Y⁻ of the ionic liquid represented by Formula 8 may includethe anionic moiety —Y⁻ as described in Formula 1.

The ionic liquid may be, for example, a compound represented by Formula10, a compound represented by Formula 11, or a combination thereof.

In Formula 10, Z may be N or P; and R₇, R₈, R₉, and R₁₀ may be eachindependently an unsubstituted or substituted C1-C30 alkyl group, anunsubstituted or substituted C6-C30 aryl group, an unsubstituted orsubstituted C2-C30 heteroaryl group, an unsubstituted or substitutedC4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30heterocycloalkyl group.

In Formula 11, Z may be N or P; and R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, andR₁₇ may be each independently hydrogen, an unsubstituted or substitutedC1-C30 alkyl group, an unsubstituted or substituted C6-C30 aryl group,an unsubstituted or substituted C2-C30 heteroaryl group, anunsubstituted or substituted C4-C30 cycloalkyl group, or anunsubstituted or substituted C3-C30 heterocycloalkyl group.

In Formula 10,

Z may be N or P; R₇, R₈, R₉, and R₁₀ may be each independently anunsubstituted or substituted C1-C30 alkyl group, an unsubstituted orsubstituted C6-C30 aryl group, an unsubstituted or substituted C2-C30heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkylgroup, or an unsubstituted or substituted C3-C30 heterocycloalkyl group;and

Y⁻ may be an anion or, for example, an anion represented by Formula 2-1or Formula 3-1.

In Formula 2-1, Rf may be a fluorine atom, an unsubstituted orsubstituted C1-C30 fluorinated alkyl group, an unsubstituted orsubstituted C6-C30 arylene group, or a combination thereof.

The ionic liquid may be, for example, a compound represented by one ofFormulae 11a, 11b, and 12 to 15, or a combination thereof.

In Formulae 11a, 11b, and 12 to 15, R₁₈ to R₂₇ may be each independentlyan unsubstituted or substituted C1-C30 alkyl group, an unsubstituted orsubstituted C6-C30 aryl group, an unsubstituted or substituted C2-C30heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkylgroup, or an unsubstituted or substituted C3-C30 heterocycloalkyl group.

In Formulae 11a, 11b, and 12 to 15, Y⁻ may be (C₂F₅SO₂)₂N⁻,(C₂FSO₂)(CF₃SO₂)N⁻, (CF₃SO₂)₂N⁻, (CN)₂N⁻, or a combination thereof, or,for example, an anion represented by Formula 2-1 or Formula 3-1.

In Formula 2-1, Rf may be a fluorine atom, an unsubstituted orsubstituted C1-C30 fluorinated alkyl group, an unsubstituted orsubstituted C6-C30 arylene group, or a combination thereof.

The ionic liquid may be at least one of a compound represented byFormulae 30 to 33.

When the compound of Formulae 31 to 34 is used as the ionic liquid,using the ion conductor of Formula 4 as an ion conductor may furtherincrease a miscibility of the cathode hybrid electrolyte.

Examples of the lithium salt of the cathode hybrid electrolyte mayinclude LiPF₆, LIBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, Li(CF₃SO₂)₃C, LiC₂F₅SO₃,Li(FSO₂)₂N, LiC₄FeSO₃, LiN(SO₂CF₂CF₃)₂, LiN(CN)₂, and a compoundrepresented by Formulae 16 to 19, and a concentration of the lithiumsalt may be in a range of about 0.01 M to about 5 M, or, for example,about 0.1 M to about 3 M or about 0.1 M to about 2 M.

A viscosity of the cathode hybrid electrolyte according to an embodimentmay be in a range of about 25 centipoise (cps) to about 450 cps, or,about 100 cps to about 450 cps, or about 300 cps to about 450 cps. Whenthe viscosity of the cathode hybrid electrolyte is within these ranges,wettability with respect to the cathode may be excellent, and leakage tothe outside may be prevented.

A weight average molecular weight of the ion conductor of Formula 1 maybe about 50,000 Dalton or greater or, for example, in a range of about50,000 Dalton to about 300,000 Dalton. When the weight average molecularweight of the ion conductor is within this range, an ion conductivity ofthe cathode hybrid electrolyte may further improve. The weight averagemolecular weight of the ion conductor may be measured by using a gelpermeation chromatography (GPC).

The ion conductivity of the cathode hybrid electrolyte according to anembodiment at 25° C. is about 0.5 Siemens per centimeter (S/cm) orhigher or, in a range of about 0.5 S/cm to about 1 S/cm, or about 0.6S/cm to about 0.8 S/cm. When the cathode including the cathode hybridelectrolyte is used, an increase of the internal resistance of the solidsecondary battery is suppressed.

A lithium ion mobility of the cathode hybrid electrolyte according to anembodiment may be about 0.5 or higher or, in a range of about 0.5 toabout 0.7, or about 0.5 to about 0.65.

According to another aspect of an embodiment, provided is a cathode fora solid secondary battery, the cathode including a cathode activematerial and the cathode hybrid electrolyte according to an embodiment.

The cathode includes a plurality of cathode active material particles,and a cathode hybrid electrolyte may be included between the pluralityof cathode active material particles.

The cathode may include a cathode active material layer including thecathode active material, and the cathode hybrid electrolyte may bedisposed in at least one of pores in the cathode active material layeror may be disposed on a surface of the cathode active material layer. Inthis regard, an interfacial resistance between the cathode activematerial particles decreases, and thus an internal resistance of thesolid secondary battery including the cathode decreases. Also, a mixturedensity of the cathode may improve. The cathode may be prepared througha process of stacking the cathode active material layer on the cathodecurrent collector and impregnating the resultant in the cathode hybridelectrolyte.

A mixture density of the cathode active material layer including thecathode active material and the cathode hybrid electrolyte may be, about3.0 grams per cubic centimeter (g/cm³) or higher, about 3.1 g/cm³ orhigher, about 3.2 g/cm³ or higher, or in a range of about 3.2 g/cm³ toabout 3.5 g/cm³. An energy density of the solid secondary batteryincluding the cathode may improve.

According to another aspect of an embodiment, provided is a solidsecondary battery including a cathode; an anode; and a solid electrolytedisposed between the cathode and the anode, wherein at least one of thecathode and the anode includes the cathode hybrid electrolyte.

The solid electrolyte may be, for example, at least one selected from asulfide-based solid electrolyte and an oxide-based, i.e., anoxide-containing solid electrolyte, but embodiments are not limitedthereto, and any material available as an inorganic solid electrolyte inthe art may be used.

The solid electrolyte may be, for example, an oxide-based solidelectrolyte. The oxide-based solid electrolyte may be, for example, atleast one selected from Li_(1+x+y)Al_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂ (where0<x<2 and 0≤y<3), BaTiO₃, Pb(Zr,Ti)O₃ (PZT),Pb_(1−x)La_(x)Zr_(1−y)Ti_(y)O₃ (PLZT) (where 0≤x<1 and 0≤y<1),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), HfO₂, SrTiO₃, SnO₂, CeO₂, Na₂O,MgO, NiO, CaO, BaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, TiO₂, SiO₂, SiC, lithiumphosphate (Li₃PO₄), lithium titanium phosphate (Li_(x)Ti_(y)(PO₄)₃)(where 0<x<2 and 0<y<3), lithium aluminum titanium phosphate(Li_(x)Al_(y)Ti_(z)(PO₄)₃) (where 0<x<2, 0<y<1, and 0<z<3),Li_(1+x+y)(Al_(a)Ga_(1−a))_(x)(Ti_(b)Ge_(1−b))_(2−x)Si_(y)P_(3−y)O₁₂(where 0≤x≤1 0≤y≤1, 0≤a≤1, and 0≤b≤1), lithium lanthanum titanate(Li_(x)La_(y)TiO₃) (where 0<x<2 and 0<y<3), lithium germaniumthiophosphate (Li_(x)Ge_(y)P_(z)S_(w)) (where 0<x<4, 0<y<1, 0<z<1, and0<w<5), lithium nitride-based glass (Li_(x)N_(y)) (where 0<x<4 and0<y<2), SiS₂ (Li_(x)Si_(y)S_(z)) (where 0<x<3, 0<y<2, and 0<z<4),P₂S₅-based glass (Li_(x)P_(y)S_(z)) (where 0<x<3, 0<y<3, and 0<z<7),Li₂O, LiF, LiOH, Li₂CO₃, LiA₂, Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂-typeceramics, and gamet-type ceramics Li_(3+x)La₃M₂O₁₂ (M=Te, Nb, or Zr)(where x is an integer of 1 to 10), or a combination thereof. Thecathode hybrid electrolyte according to an embodiment may have a reducedreactivity to an oxide-based solid electrolyte and thus may suppress aside reaction therebetween.

The inorganic solid electrolyte may be, for example, a sulfide-basedsolid electrolyte. The sulfide-based solid electrolyte may be, forexample, at least one selected from Li₂S—P₂S₅ or Li₂S—P₂S₅—LiX (where Xis a halogen atom), Li₂S—P₂S₅—Li₂O, Li₂S—P₂S₅—Li₂O—LiI, Li₂S—SiS₂,Li₂S—SiS₂—LiI, Li₂S—SiS₂—LiBr, Li₂S—SiS₂—LiCl, Li₂S—SiS₂—B₂S₃—LiI,Li₂S—SiS₂—P₂S₅—LiI, Li₂S—B₂S₃, Li₂S—P₂S₅—Z_(m)S_(n) (where m and n areeach a positive integer; and Z is one of Ge, Zn, and Ga), Li₂S—GeS₂,Li₂S—SiS₂—Li₃PO₄, Li₂S-SiS₂Li_(p)MO_(q) (where p and q are each apositive integer and M is one of P, Si, Ge, B, A, Ga, and In),Li_(7−x)PS_(6−x)Cl, (where 0≤x≤2), Li_(7-x)PS_(6−x)Br, (where 0≤x≤2),and Li_(7−x)PS_(6−x)I_(x) (where 0≤x≤2). When the organic salt is used,a reactivity of the sulfide-based solid electrolyte and the organic saltmay significantly decrease.

An oxidation current density of the cathode hybrid electrolyte accordingto an embodiment measured by using Linear Sweep Voltammetry (LSV) at 25°C. is 1×10⁻⁵ A/cm² or lower versus a lithium metal until 4.3 V. Forexample, a voltage of the hybrid electrolyte having an oxidation currentdensity measured by LSV at 25° C. of 1×10⁻⁵ A/cm² or lower versus alithium metal is about 3.2 V or higher, about 3.5 V or higher, about 4.0V or higher, about 4.1 V or higher, about 4.2 V or higher, about 4.3 Vor higher, about 4.5 V or higher, or about 5.0 V or higher. A voltage ofthe hybrid electrolyte may be, for example, in a range of about 3.2 V toabout 5 V.

When the cathode hybrid electrolyte includes an electrochemically stablevoltage window of a wide range, cycle characteristics of the solidsecondary battery including the hybrid electrolyte may, for example,improve within a high voltage range.

The cathode active material may include, for example, a lithiumtransition metal oxide having a layered rock-salt structure. In someembodiments, the electrode may be, for example, an anode including ananode active material. The anode active material may include, forexample, amorphous carbon, crystalline carbon, metal, or metalloid thatmay form an alloy or a compound with lithium.

FIG. 5 shows a structure of the solid secondary battery according to anembodiment.

Referring to FIG. 5, a solid secondary battery 1 includes an anode 20including an anode active material layer 22; a cathode 10 including acathode active material layer 12; and a solid electrolyte 30 disposedbetween the anode 20 and the cathode 10.

Cathode

The cathode 10 includes a cathode current collector 11 and the cathodeactive material layer 12. The cathode 10 may include the cathode hybridelectrolyte described above. Although not shown in FIG. 5, the cathodehybrid electrolyte may exist at an interface between the cathode 10 andthe solid electrolyte 30 or may exist around the cathode 10 in asolidified state.

The cathode active material layer 12 may include, for example, a cathodeactive material and a cathode hybrid electrolyte. The cathode activematerial is a cathode active material capable of reversibly absorbingand desorbing lithium ions. The cathode active material may be, forexample, a lithium transition metal oxide such as a lithium cobalt oxide(LCO), a lithium nickel oxide, a lithium nickel cobalt oxide, a lithiumnickel cobalt aluminum oxide (NCA), a lithium nickel cobalt manganate(NCM), a lithium manganate, or a lithium iron phosphate; a nickelsulfide; a copper sulfide; a lithium sulfide; an iron oxide; or avanadium oxide, but embodiments are not limited thereto, and anymaterial available as a cathode active material in the art may be used.Examples of the cathode active material may be used alone or in amixture of at least two selected therefrom. The cathode active materialmay be, for example, a lithium cobalt oxide (LCO) which has excellenthigh-voltage stability.

The lithium transition metal oxide may be, for example, a compoundrepresented by one of the following formulae:

Li_(a)A_(1−b)B′_(b)D₂ (where 0.90≤a≤1 and 0≤b≤0.5);Li_(a)E_(1−b)EB′_(b)O_(2−c)D_(c) (where 0.90≤a≤1, 0≤b≤0.5, and0≤c≤0.05); LiE_(2−b)B′_(b)O_(4−c)D_(c) (where 0≤b≤0.5 and 0≤c≤0.05);Li_(a)Ni_(1−b−c)Co_(b)B′_(b)D_(α) (where 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05,and 0<α≤2); Li_(a)Ni_(1−b−c)Co_(b)B′_(c)O²⁻⁺F′_(α) (where 0.90≤a≤1,0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Co_(b)B′_(c)O_(2−α)F′₂(where 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2);Li_(a)Ni_(1−b−c)Mn_(b)B′_(c)D_(α) (where 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05,and 0<α≤2); Li_(a)Ni_(1−b−c)Mn_(b)B′_(c)O_(2−α)F′_(α) (where 0.90≤a≤1,0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Mn_(b)B′_(c)O_(2−α)F′₂(where 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li_(a)Ni_(b)E_(c)G_(d)O₂(where 0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, and 0.001≤d≤0.1);Li_(a)Ni_(b)Co_(e)Mn_(d)G_(e)O₂ (where 0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5,0≤d≤0.5, and 0.001≤e≤0.1); Li_(a)NiG_(b)O₂ (where 0.90≤a≤1 and0.001≤b≤0.1); Li_(a)CoG_(b)O₂ (where 0.90≤a≤1 and 0.001≤b≤0.1);Li_(a)MnG_(b)O₂ (where 0.90≤a≤1 and 0.001≤b≤0.10); Li_(a)Mn₂G_(b)O₄(where 0.90≤a≤1 and 0.001≤b≤0.1); QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅; LiI′O₂;LiNiVO₄; Li_((3−f))J₂(PO₄)₃ (where 0≤f≤2); Li_((3−f))Fe₂(PO₄)₃ (where0≤f≤2); and LiFePO₄. In the compound, A may be nickel (Ni), cobalt (Co),manganese (Mn), or a combination thereof; B′ may be aluminum (Al),nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), iron (Fe),magnesium (Mg), strontium (Sr), vanadium (V), a rare earth element, or acombination thereof; D may be oxygen (O), fluorine (F), sulfur (S),phosphorus (P), or a combination thereof; E may be cobalt (Co),manganese (Mn), or a combination thereof; F′ may be fluorine (F), sulfur(S), phosphorus (P), or a combination thereof; G may be (Al), chromium(Cr), manganese (Mn), iron (Fe), magnesium (Mg), lanthanum (La), cerium(Ce), strontium (Sr), vanadium (V), or a combination thereof; Q may betitanium (Ti), molybdenum (Mo), manganese (Mn), or a combinationthereof; I′ may be chromium (Cr), vanadium (V), iron (Fe), scandium(Sc), yttrium (Y), or a combination thereof; and J may be vanadium (V),chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), ora combination thereof. The compounds may have a surface coating layer(hereinafter, also referred to as “coating layer”).

Alternatively, a mixture of a compound without a coating layer and acompound having a coating layer, the compounds being selected from thecompounds listed above, may be used. In some embodiments, the coatinglayer may include at least one compound of a coating element of oxide,hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of thecoating element.

In some embodiments, the compounds for the coating layer may beamorphous or crystalline. In some embodiments, the coating element forthe coating layer may be magnesium (Mg), aluminum (Al), cobalt (Co),potassium (K), sodium (Na), calcium (Ca), silicon (Si), titanium (Ti),vanadium (V), tin (Sn), germanium (Ge), gallium (Ga), boron (B), arsenic(As), zirconium (Zr), or a mixture thereof. In some embodiments, thecoating layer may be formed using any method that does not significantlyadversely affect the physical properties of the cathode active materialwhen a compound of the coating element is used. For example, the coatinglayer may be formed using a spray coating method or a dipping method.The coating methods may be well understood by one of ordinary skill inthe art, and thus a detailed description thereof will be omitted.

The cathode active material may include, for example, a lithium salt ofa transition metal oxide that has a layered rock-salt type structureamong the examples of the lithium transition metal oxide. For example,the “layered rock-salt type structure” refers to a structure in which anoxygen atom layer and a metal atom layer are alternately and regularlyarranged in a 111 direction in a cubic rock-salt type structure, whereeach of the atom layers forms a two-dimensional flat plane. The “cubicrock-salt type structure” refers to a sodium chloride (NaCl) typestructure, which is one of the crystalline structures, in particular, toa structure in which face-centered cubic (fcc) lattices respectivelyformed of anions and cations are shifted by only a half of the ridge ofeach unit lattice. Examples of the lithium transition metal oxide havingthe layered rock-salt type structure may include a ternary lithiumtransition metal oxide expressed as LiNi_(x)Co_(y)Al_(z)O₂ (NCA) orLiNi_(x)Co_(y)MnO₂ (NCM) (where 0<x<1, 0<y<1, 0<z<1, and x+y+z=1). Whenthe cathode active material includes a ternary transition metal oxidehaving the layered rock-salt type structure, an energy density andthermal stability of the solid secondary battery 1 may improve.

The cathode active material may be, for example, a lithium cobalt oxide(LCO) having excellent high-voltage stability.

The cathode active material may be covered by a coating layer asdescribed above. The coating layer is any material that may be used as acoating layer of a cathode active material of a solid secondary batteryin the art. The coating layer may be, for example, Li₂O—ZrO₂.

When the cathode active material includes nickel (Ni) as a ternarylithium transition metal oxide such as NCA or NCM, a capacity density ofthe solid secondary battery 1 increases, and thus metal elution from thecathode active material in a charged state may be reduced. As a result,the solid secondary battery 1 according to an embodiment may haveimproved cycle characteristics in a charged state.

A shape of the cathode active material may be, for example, particulateshapes such as a true spherical shape, an elliptical shape, or aspherical shape. A particle diameter of the cathode active material isnot particularly limited but may be in a range applicable to a cathodeactive material of a conventional solid secondary battery. An amount ofthe cathode active material of the cathode 10 is not particularlylimited and may be in a range applicable to a cathode layer of aconventional solid secondary battery.

The cathode current collector 11 may be, for example, a plate or a foilthat is formed of indium (In), copper (Cu), magnesium (Mg), stainlesssteel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn),aluminum (A), germanium (Ge), lithium (Li), or an alloy thereof. Thecathode current collector 11 may be omitted.

Additives such as a conducting agent, a binder, a filler, a dispersant,and an ion conducting agent may be added to the cathode 10 in additionto the cathode active material and the solid electrolyte. Examples ofthe conducting agent are acetylene black, ketjen black, naturalgraphite, artificial graphite, carbon black, carbon fiber; metal powderor metal fiber of copper, nickel, aluminum, or silver; and a conductivematerial, such as a polyphenylene derivative, which may be used alone oras a mixture thereof. Examples of the binder are a vinylidenefluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF),polyacrylonitrile, polymethylmethacrylate, polytetrafluoroethylene,mixtures thereof, and a styrene butadiene rubber polymer. The coatingagent, the dispersant, and the ion conducting agent that may beappropriately added to the cathode 10 may be commonly known materialsthat are generally used in an electrode of a solid secondary battery inthe art.

A thickness of the cathode may be in a range of about 0.1 μm to about100 μm. A thickness of the solid electrolyte may be in a range of about1 nm to about 1000 μm, for example, about 0.1 μm to about 100 μm, forexample, about 0.5 μm to about 70 μm, for example, about 1 μm to about50 μm, or, for example, about 1 μm to about 20 μm.

Anode

The anode 20 includes an anode current collector layer 21 and an anodeactive material layer 22. An anode active material in the anode activematerial layer 22 may be, for example, in the form of particles. Anaverage particle diameter of the anode active material in the form ofparticles may be, for example, about 4 μm or less, about 3 μm or less,about 2 μm or less, about 1 μm or less, or about 900 nm or less. Anaverage particle diameter of the anode active material in the form ofparticles may be, for example, in a range of about 10 nm to about 4 μm,about 10 nm to about 3 μm, about 10 nm to about 2 μm, about 10 nm toabout 1 μm, or about 10 nm to about 900 nm. Due to the anode activematerial having an average particle diameter within these ranges,reversible absorbing and/or desorbing of lithium duringcharging/discharging may further be facilitated. The average particlediameter of the anode active material may be a median diameter (D50)measured by using a laser-diffraction particle size distribution meter.

The anode active material in the anode active material layer 22 may be,for example, a carbonaceous anode active material and/or anoncarbonaceous anode active material.

Examples of the carbonaceous anode active material may includecrystalline carbon, amorphous carbon, and mixtures thereof. Examples ofthe crystalline carbon are graphite, such as natural graphite orartificial graphite that are non-shaped or in plate, flake, spherical,or fibrous form, and examples of the amorphous carbon are soft carbon(carbon sintered at low temperatures), hard carbon, meso-phase pitchcarbides, and sintered cokes. Examples of the amorphous carbon mayinclude carbon black (CB), acetylene black (AB), furnace black (FB),ketjen black (KB), and graphene, but embodiments are not limitedthereto, and any material available as amorphous carbon in the art maybe used.

A metal or a metalloid anode active material may include at least one ofgold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag),aluminum (A), bismuth (Bi), tin (Sn), or zinc (Zn), but embodiments arenot limited thereto, and any material available as a metal anode activematerial or a metalloid anode active material that forms an alloy or acompound with lithium in the art may be used. For example, nickel (Ni)does not form an alloy with lithium and thus is not a metal anode activematerial.

The anode active material in the anode active material layer 22 may be anon-carbonaceous anode active material. For example, thenon-carbonaceous anode active material is at least one of a metalalloyable with lithium, an alloy of a metal alloyable with lithium, oran oxide of a metal alloyable with lithium. Examples of the metalalloyable with lithium may be Si, Sn, A, Ge, Pb, Bi, Sb, a Si—Y alloy(where Y is an alkali metal, an alkali earth metal, Group XIII to XIVelements, a transition metal, a rare earth element, or a combinationthereof, and Y is not Si), and a Sn—Y alloy (where Y is an alkali metal,an alkali earth metal, Group XIII to XIV elements, a transition metal, arare earth element, or a combination thereof, and Y is not Sn). In someembodiments, Y may be magnesium (Mg), calcium (Ca), strontium (Sr),barium (Ba), radium (Ra), scandium (Sc), yttrium (Y), titanium (Ti),zirconium (Zr), Hf, Rf, V, Nb, Ta, Db, chromium (Cr), molybdenum (Mo),tungsten (W), seaborgium (Sg), technetium (Tc), rhenium (Re), bohrium(Bh), iron (Fe), lead (Pb), ruthenium (Ru), osmium (Os), hassium (Hs),rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), copper (Cu),silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), boron (B), aluminum(Al), gallium (Ga), tin (Sn), indium (In), germanium (Ge), phosphorus(P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium(Se), tellurium (Te), polonium (Po), or a combination thereof. Examplesof the transition metal oxide may include a lithium titanium oxide, avanadium oxide, and a lithium vanadium oxide. Examples of thenon-transition metal oxide may include SnO₂ and SiO_(x) (where 0<x<2).Examples of the non-carbonaceous anode active material may include atleast one of Si, Sn, Pb, Ge, A, SiO, (where 0<x≤2), SnO_(y) (where0<y≤2), Li₄Ti₅O₁₂, TiO₂, LiTiO₃, or Li₂Ti₃O₇, but embodiments are notlimited thereto, and any material available as an uncarbonaceous anodeactive material in the art may be used.

The anode current collector 21 may be, for example, formed of a materialthat does not react with lithium, that is, a material that neither formsan alloy nor a compound. Examples of the material forming the anodecurrent collector 21 may include copper (Cu), stainless steel, titanium(Ti), iron (Fe), cobalt (Co), and nickel (Ni), but embodiments are notlimited thereto, and any material available as an electrode currentcollector in the art may be used. The anode current collector 21 may beformed of one of those examples of the metal or may be formed of analloy or a coating material of at least two metals. The anode currentcollector 21 may be, for example, in the form of plate or foil.

The anode active material layer 22 may further include additives used inthe conventional solid secondary battery 1, such as a filler, adispersant, a conducting agent, and a binder. The anode active materiallayer 22 may be, for example, formed using a filler, a dispersant, aconducting agent, and a binder used in the cathode active material layer12.

Solid Electrolyte

The electrolyte 30 includes the solid electrolyte 30 disposed betweenthe cathode 10 and the anode 20 as shown in FIG. 5. The solidelectrolyte 30 may or may not include a hybrid electrolyte.

The solid electrolyte is, for example, a sulfide-based solidelectrolyte. Examples of the sulfide-based solid electrolyte may includeat least one selected from Li₂S—P₂S₅, Li₂S—P₂S₅—LiX (where X is ahalogen), Li₂S—P₂S₅—Li₂O, Li₂S—P₂S₅—Li₂O—LiI, Li₂S—SiS₂, Li₂S—SiS₂—LiI,Li₂S—SiS₂—LiBr, Li₂S—SiS₂—LiCl, Li₂S—SiS₂—B₂S₃—LiI, Li₂S—SiS₂—P₂S₅—LiI,Li₂S—B₂S₃, Li₂S—P₂S₅—Z_(m)S_(n) (where m and n are each a positiveinteger, and Z is one of Ge, Zn, and Ga), Li₂S—GeS₂, Li₂S—SiS₂—Li₃PO₄,and Li₂S—SiS₂-Li_(p)MO_(q) (where p and q are each a positive integer,and M is one of P, Si, Ge, B, Al, Ga, and In). For example, thesulfide-based solid electrolyte material may be prepared by melting andquenching starting materials (e.g., Li₂S or P₂S₅), or mechanical millingthe starting materials. Subsequently, the sulfide-based electrode may beheat-treated. The sulfide-based solid electrolyte may be amorphous orcrystalline and may be a mixed form thereof.

Also, the solid electrolyte 30 may include sulfur (S), phosphorus (P),and lithium (Li), as component elements in the sulfide-based solidelectrolyte material. For example, the solid electrolyte 30 may be amaterial including Li₂S—P₂S₅. When Li₂S—P₂S₅ is used as a sulfide-basedsolid electrolyte material that forms the solid electrolyte 30, a mixedmolar ratio of Li₂S and P₂S₅ (Li₂S:P₂S₅) may be, for example, in a rangeof about 50:50 to about 90:10. Particularly, the sulfide-based solidelectrolyte in the solid electrolyte 30 may be an argyrodite-typecompound including at least one selected from Li_(7−x)PS_(6−x)Cl_(x)(where 0≤x≤2), Li_(7−x)PS_(6−x)Br_(x) (where 0≤x≤2), andLi_(7−x)PS_(6−x)I_(x) (where 0≤x≤2). Examples of the argyrodite-typesulfide-based solid electrolyte may include Li₆PS₅Cl, Li₆PS₅Br, orLi₆PS₅I.

Alternatively, the solid electrolyte 30 may be, for example, anoxide-based solid electrolyte. The oxide-based solid electrolyte may be,for example, at least one selected fromLi_(1+x+y)Al_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂ (where 0<x<2 and 0≤y<3),BaTiO₃, Pb(Zr,Ti)O₃ (PZT), Pb_(1−b)La_(x)Zr_(1−y)Ti_(y)O₃ (PLZT) (where0≤x<1 and 0≤y<1), Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), HfO₂, SrTiO₃,SnO₂, CeO₂, Na₂O, MgO, NiO, CaO, BaO, ZnO, ZrO₂, Y₂O₃, A₂O₃, TiO₂, SiO₂,SiC, lithium phosphate (LiPO₄), lithium titanium phosphate(Li_(x)Ti_(y)(PO₄)₃) (where 0<x<2 and 0<y<3), lithium aluminum titaniumphosphate (Li_(x)Al_(y)Ti_(z)(PO₄)₃) (where 0<x<2, 0<y<1, and 0<z<3),Li_(1+x+y)(Al_(a)Ga_(1−a))_(x)(Ti_(b)Ge_(1−b))_(2−x)Si_(y)P_(3−y)O₁₂(where 0≤x≤1 0≤y≤1, 0≤a≤1, and 0≤b≤1), lithium lanthanum titanate(Li_(x)La_(y)TiO₃) (where 0<x<2 and 0<y<3), lithium germaniumthiophosphate (Li_(x)Ge_(y)P_(z)S_(w)) (where 0<x<4, 0<y<1, 0<z<1, and0<w<5), lithium nitride-based glass (Li_(x)N_(y)) (where 0<x<4 and0<y<2), SiS₂ (Li_(x)Si_(y)S_(z)) (where 0<x<3, 0<y<2, and 0<z<4),P₂S₅-based glass (Li_(x)P_(y)S_(z)) (where 0<x<3, 0<y<3, and 0<z<7),Li₂O, LiF, LiOH, Li₂CO₃, LiAO₂, Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂-typeceramics, and gamet-type ceramics Li_(3+x)La₃M₂O₁₂ (M=Te, Nb, or Zr)(where x is an integer of 1 to 10), or a combination thereof. Theoxide-based solid electrolyte may be amorphous or crystalline and may bea mixed form thereof.

For example, the solid electrolyte 30 may further include a binder.Examples of the binder included in the solid electrolyte layer 30 may bestyrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidenefluoride, or polyethylene, but embodiments are not limited thereto, andany material available as a binder in the art may be used. The binder ofthe solid electrolyte 30 may be the same with or different from a binderof the cathode active material layer 12 and the anode active materiallayer 22.

For example, the cathode 10, the anode 20, and the solid electrolyte 30are each prepared separately and then stacked to prepare the solidsecondary battery 1.

Preparation of Cathode

Materials constituting the cathode active material layer 12, such as acathode active material, a conducting agent, and a binder, are mixed toprepare a slurry. The thus-prepared slurry is coated and dried on thecathode current collector 11 to form a cathode active material layer. Apressure is applied to the stack if needed to prepare a cathode 10. Theapplying of the pressure may be performed by using a roll press, a flatpress, or a hydrostatic press, but embodiments are not limited thereto,and any method of applying pressure that is available in the art may beused. The applying of the pressure may be omitted. The mixture of thematerials constituting the cathode active material layer 12 isdensification-molded in the form of a pellet or extension-molded in theform of sheet to prepare a cathode 10. When the cathode 10 is preparedin this manner, the cathode current collector 11 may be omitted.

A hybrid electrolyte composition including a monomer represented byFormula 20 and an ionic liquid is provided to the cathode.

The hybrid electrolyte composition may further include a lithium salt.

Subsequently, heat or light is applied to the provided hybridelectrolyte composition to perform a polymerization reaction.

In Formula 20, X is an unsubstituted or substituted C6-C30 arylenegroup, an unsubstituted or substituted C2-C30 heteroarylene group, or—C(═O)O—R₇—, R₇ is an unsubstituted or substituted C1-C30 alkylene groupor an unsubstituted or substituted C6-C30 arylene group, R₁ to R₃ areeach independently a hydrogen, an unsubstituted or substituted C1-C20alkyl group, an unsubstituted or substituted C6-C20 aryl group, or anunsubstituted or substituted C2-C30 heteroaryl group, and —Y⁻ is ananionic moiety.

In some embodiments, the polymerization reaction is performed byheat-treatment. The heat-treatment varies depending on a type of themonomer of Formula 20 and is performed, for example, at a temperature ina range of about 40° C. to about 90° C.

Examples of the monomer of Formula 20 may include monomers representedby Formulae 22 to 27.

The monomer of Formula 20 may be obtained by reacting a compound ofFormula 21, with a precursor of the anionic moiety, e.g., with YH, inthe presence of a base and then performing a reaction to introducelithium to the product of the reaction.

In Formula 21, X is an unsubstituted or substituted C6-C30 arylenegroup, an unsubstituted or substituted C2-C30 heteroarylene group, or—C(═O)O—R₇—, R₇ is an unsubstituted or substituted C1-C30 alkylene groupor an unsubstituted or substituted C6-C30 arylene group, R₁ to R₃ areeach independently a hydrogen, an unsubstituted or substituted C1-C20alkyl group, an unsubstituted or substituted C6-C20 aryl group, or anunsubstituted or substituted C2-C30 heteroaryl group, and X′ is ahalogen atom. Examples of the halogen atom may include Cl, Br, and I.

Examples of the compound of Formula 21 may include a compound of Formula28 or a compound of Formula 29.

Preparation of Anode

Materials constituting the anode active material layer 22, such as ananode active material, a conducting agent, and a binder, are added to apolar solvent or a nonpolar solvent to prepare a slurry. The preparedslurry is coated and dried on the anode current collector 21 to form astack. An anode 20 is prepared by pressuring the dried stack. Thepressuring may be performed by using a roll press or a flat press, butembodiments are not limited thereto, and any press available in the artmay be used. The pressuring may be performed at, for example, roomtemperature to about 90° C. or lower or at a temperature in a range ofabout 20° C. to about 90° C. In some embodiments, the pressuring may beperformed at a high temperature of about 100° C. or higher. Thepressuring may be omitted. The mixture of the materials constituting theanode active material layer 22 is densification-molded in the form of apellet or extension-molded in the form of sheet to prepare an anode 20.When the anode 20 is prepared in this manner, the anode currentcollector 21 may be omitted.

Preparation of Solid Electrolyte

The solid electrolyte 30 is prepared by using a solid electrolyte formedof, for example, an oxide-based solid electrolyte material.

The solid electrolyte may be deposited by using a common layerdeposition method such as an aerosol deposition method, a cold spraymethod, or a sputtering method to prepare the solid electrolyte 30. Insome embodiments, the solid electrolyte 30 may be prepared by applyingpressure to a mass of solid electrolyte particles. In some embodiments,the solid electrolyte 30 may be prepared by mixing a solid electrolyte,a solvent, and a binder and performing coating, drying, and pressuringprocesses.

Preparation of Solid Secondary Battery

The cathode 10, anode 20, and solid electrolyte 30 prepared as describedabove were stacked and had pressure applied so that the solidelectrolyte 30 is between the cathode 10 and the anode 20, therebypreparing the solid secondary battery 1. The applying of pressure may beomitted. For example, the solid electrolyte 20 is disposed on thecathode to prepare a stack. Subsequently, the anode 20 is disposed onthe stack such that the solid electrolyte 30 and the anode activematerial layer are adjacent, and the stack is pressed to prepare a solidsecondary battery 1. The applying of pressure may be performed using aroll press, a flat press, or a hydrostatic press, but embodiments arenot limited thereto, and any method of applying pressure available inthe art may be used. The applying of pressure may be performed at, forexample, room temperature to about 90° C. or lower or at a temperaturein a range of about 20° C. to about 90° C. In some embodiments, theapplying of pressure may be performed at a high temperature of about100° C. or higher. Due to the applying of pressure, for example, a solidelectrolyte powder is sintered, and thus one solid electrolyte isformed.

A composition and a preparation method of the solid secondary battery 1are examples of various embodiments, where elements of the compositionand process of the preparation may be appropriately modified.

Hereinafter, a method of preparing the cathode according to anembodiment will be described in detail.

According to an embodiment, a composite cathode active material, aconducting agent, and a binder are mixed in a solid state to prepare acathode.

The binder may be the same as that used in the solid electrolyte asdescribed above. As the binder, the same binder that is commonly used ina lithium battery may be added. Examples of the binder may include athermoplastic polymer or a thermosetting resin. For example,polyethylene, polypropylene, polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), a styrene-butadiene rubber, atetrafluoroethylene-perfluoroalkylvinylether co-polymer, a vinylidenefluoride-hexafluoropropyleneco-polymer,avinylidenefluoride-chlorotrifluoroethyleneco-polymer, anethylene-tetrafluoroethyleneco-polymer,polychlorotrifluoroethylene, a vinylidene fluoride-pentafluoropropyleneco-polymer, a propylene-tetrafluoroethylene co-polymer, anethylene-chlorotrifluoroethyleneco-polymer,avinylidenefluoride-hexafluoropropylene-tetrafluoroethyleneco-polymer,a vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethyleneco-polymer, an ethylene-acrylic acid copolymer may be used alone or incombination.

In some embodiments, a solvent may be added to the composite cathodeactive material, conducting agent, and binder in the preparation of thecathode to obtain a cathode active material composition, and the cathodeactive material composition may be coated and dried on a cathode currentcollector to prepare a cathode. In some embodiments, the cathode activematerial composition may be cast onto a separate support to form acathode active material layer, e.g., a film, which may then be separatedfrom the support and laminated on a metallic current collector toprepare a cathode.

Examples of performing the lamination may include a solvent castingmethod.

Referring to FIG. 5, a solid secondary battery 1 according to anembodiment will be described.

The solid secondary battery 1 may include a cathode 10, an anode 20, anda solid electrolyte 30 between the cathode 10 and the anode 20.

After the solid electrolyte 30 is disposed between the cathode 10 andthe anode 20, applying pressure to the resultant stack may be performedto prepare the solid secondary battery 1. The applying of pressure maybe omitted.

When used, the applying of pressure may be performed by using, forexample, a roll press, a flat press, or a hydrostatic press, butembodiments are not limited thereto, and any method of applying pressurethat is available in the art may be used. The applying of pressure maybe performed at, for example, in a range of about 20° C. to about 90° C.In some embodiments, the applying of pressure may be performed at a hightemperature of about 100° C. or higher. For example, due to the applyingof pressure, the solid electrolyte powder is sintered, and thus onesolid electrolyte may be formed.

A composition and a preparation method of the solid secondary battery 1are examples of various embodiments, where elements of the compositionand process of the preparation may be appropriately modified.

Definitions of substituents used in the formulae of the presentspecification are as follows.

The term “alkyl” refers to a fully saturated branched or unbranched(straight chain or linear) hydrocarbon group. Examples of the alkylgroup are a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group,an n-pentyl group, an isopentyl group, a neopentyl group, an iso-amylgroup, an n-hexyl group, a 3-methylhexyl group, a 2,2-dimethylpentylgroup, a 2,3-dimethylpentyl group, and an n-heptyl group.

The term “substituted” refers to a group, such as an alkyl group, whereat least one hydrogen is replaced with a halogen atom, a C1-C30 alkylgroup substituted with a halogen atom (e.g., CF₃, CH₃CF₂, CH₂F, orCCl₃), a C1-C30 alkoxy group, a C2-C30 alkoxyalkyl group, a hydroxylgroup, a nitro group, a cyano group, an amino group, an alkylaminogroup, an amidino group, a hydrazine, a hydrazone, a carboxyl group or asalt thereof, a sulfonyl group, a sulfamoyl group, a sulfonic acid groupor a salt thereof, a phosphoric acid or a salt thereof, a C1-C30 alkylgroup, a C2-C30 alkenyl group, a C2-C30 alkynyl group, a C1-C30heteroalkyl group, a C6-C30 aryl group, a C7-C30 arylalkyl group, aC2-C30 heteroaryl group, a C3-C30 heteroarylalkyl group, a C2-C30heteroaryloxy group, or a C2-C30 heteroaryloxyalkyl group. The totalnumber of carbon atoms listed in a group does not include anysubstituents, e.g., a —CH₂CN group is a C1 alkyl group substituted witha nitrile.

The term “alkenyl” refers to an aliphatic hydrocarbon having at leastone carbon-carbon double bond, and the term “alkynyl” refers to analiphatic hydrocarbon having at least one carbon-carbon triple bond.

The term “cycloalkyl” refers to an aliphatic hydrocarbon having at leastone carbocyclic ring. Here, the alkyl is the same as defined above. Theterm “heterocycloalkyl” refers to a cyclic alkyl group including atleast one heteroatom selected from N, O, P, and S. Here, the cycloalkylgroup is the same as defined above.

Examples of the halogen atom include fluorine, bromine, chlorine, andiodine.

The term “alkoxy” refers to “alkyl-O—”, where the alkyl is the same asdefined above. Examples of the alkoxy group may include a methoxy group,an ethoxy group, a propoxy group, a 2-propoxy group, a butoxy group, atert-butoxy group, a pentyloxy group, a hexyloxy group, a cyclopropoxygroup, and a cyclohexyloxy group. At least one hydrogen atom in thealkoxy group may be substituted with the same substituent in the case ofthe alkyl group described above.

The term “cycloalkyloxy” refers to “cycloalkyl-O—”, where the cycloalkylis the same as defined above. The term “heterocycloalkyloxy” refers to“heterocycloalkyl-O—”, where the heterocycloalkyl is the same as definedabove.

The term “aryl” group may be used alone or as a combination and refersto an aromatic hydrocarbon including at least one ring. The aryl groupincludes a group in which an aromatic ring is optionally fused to atleast one cycloalkyl ring. Examples of the aryl group may include aphenyl group, a naphthyl group, and a tetrahydronaphthyl group. Also, atleast one hydrogen atom in the aryl may be substituted with the samesubstituent in the case of the alkyl.

The term “arylalkyl” refers to an alkyl group substituted with an arylgroup, where the alkyl and the aryl are the same as defined above. Anexample of an arylalkyl group is a benzyl group.

The term “aryloxy” refers to “aryl-O—”, where the aryl is the same asdefined above.

The term “arylthio” refers to “aryl-S—”, where the aryl is the same asdefined above.

The term “heteroaryl” group refers to a monocyclic or bicyclic organiccompound that contains at least one heteroatom (e.g., N, O, P, S, or Si)where the remaining ring atoms are carbon atoms. The heteroaryl groupmay include, for example, 1 to 5 heteroatoms, and 5 to 10 ring members.S or N may be oxidized to various oxidation states.

Examples of the monocyclic heteroaryl group may include a thienyl group,a furyl group, a pyrrolyl group, an imidazolyl group, a pyrazolyl group,a thiazolyl group, an isothiazolyl group, a 1,2,3-oxadiazolyl group, a1,2,4-oxadiazolyl group, a 1,2,5-oxadiazolyl group, a 1,3,4-oxadiazolylgroup, a 1,2,3-thiadiazolyl group, a 1,2,4-thiadiazolyl group, a1,2,5-thiadiazolyl group, a 1,3,4-thiadiazolyl group, an isothiazol-3-ylgroup, an isothiazol-4-yl group, an isothiazol-5-yl group, anoxazol-2-yl group, an oxazol-4-yl group, an oxazol-5-yl group, anisooxazol-3-yl group, an isooxazol-4-yl group, an isooxazol-5-yl group,a 1,2,4-triazol-3-yl group, a 1,2,4-triazol-5-yl group, a1,2,3-triazol-4-yl group, a 1,2,3-triazol-5-yl group, a tetrazolylgroup, a pyrid-2-yl group, a pyrid-3-yl group, a 2-pyrazin-2yl group, apyrazin-4-yl group, a pyrazin-5-yl group, a 2-pyrimidin-2-yl group, a4-pyrimidin-2-yl group, and a 5-pyrimidin-2-yl group.

As used herein, the term “heteroaryl” refers to a group in which aheteroaromatic ring is optionally fused to at least one aryl,cycloaliphatic, or heterocyclic ring.

Examples of the bicyclic heteroaryl group may include an indolyl group,an isoindolyl group, an indazolyl group, an indolizinyl group, a purinylgroup, a quinolizinyl group, a quinolinyl group, and an isoquinolinylgroup. At least one hydrogen atom of the heteroaryl group may besubstituted with the same substituent in the case of the alkyl groupdescribed above.

The term “heteroarylalkyl” refers to an alkyl group substituted with aheteroaryl group where the alkyl group and the heteroaryl group are thesame as defined above.

The term “heteroaryloxy” refers to “heteroaryl-O—”, where the heteroarylis the same as defined above. Also, the term “heteroarylthio” refers to“heteroaryl-S—”, where the heteroaryl is the same as defined above.

The term “alkylene”, “arylene”, “heteroarylene”, “cycloalkylene”, and“heterocycloalkylene” refer to the alkyl group, the aryl group, theheteroaryl group, the cycloalkyl group, and the heterocycloalkyl group,each respectively, in which one hydrogen atom is substituted with aradical.

Hereinafter, one or more embodiments will be described in detail withreference to the following examples and comparative examples. Theseexamples are not intended to limit the purpose and scope of the one ormore embodiments.

EXAMPLES Preparation Example 1

45 mmol of 4-vinylbenzenesulfonyl chloride (A1) and 40 mmol of CF₃SO₂NHKwere maintained in CH₃CN at 0° C. and were reacted. Subsequently, 45mmol of pyridine was added to the reaction mixture, and the resultantwas stirred at 65° C. for 48 hours. Once the reaction was complete, acompound (B) was obtained.

The obtained compound (B) was purified, and 28 mmol of K₂CO₃ was addedthereto and stirred for 5 hours. Then, a solid obtained after removing asolvent from the resultant was purified with acetone to obtain 10.5 g ofa compound C (KSTFSI).

CH₃CN and LiClO₄ were added to the compound C (KSTFSI) under ananhydrous condition to substitute K with an Li ion, and thus 7.8 g ofLISTFSI was obtained.

Preparation Example 2

In a reactor, 45 mmol of methacryloxypropyl sulfonyl chloride (A2) and40 mmol of CF₃SO₂NHK were maintained in CH₃CN at 0° C. and were reacted.Subsequently, 45 mmol of pyridine was added to the reaction mixture, andthe resultant was stirred at 65° C. for 48 hours. Once the reaction wascomplete, a compound (B2) was obtained.

The thus-obtained compound (B2) was purified, and 28 mmol of K₂CO₃ wasadded thereto and stirred for 5 hours. Then, a solid obtained afterremoving a solvent from the resultant was purified with acetone toobtain 10.5 g of a compound C2 (KMAPTFSI).

CH₃CN and LiClO₄ were added to the compound C2 (KMAPTFSI) under ananhydrous condition to substitute K with an Li ion, and thus 72 g of acompound (D) LiMAPTFSI was obtained.

Preparation of Hybrid Electrolyte Composition Example 1

N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide(PYR13TFSI) as an ionic liquid and lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI) as a lithium salt were mixedto prepare a mixture, then LiSTFSI prepared in Preparation Example 1,was added to the mixture, and the resultant was stirred at roomtemperature (25° C.) to obtain a hybrid electrolyte composition. Themixing weight ratio of the ionic liquid, PYR13TFSI, to the lithium salt,LiTFSI, was 10:100. After polymerization as described below, a polymerof Formula 6 was obtained.

In Formula 6, n is about 200.

Example 2

A hybrid electrolyte composition was obtained in the same manner as inExample 1, except that a mixing weight ratio of PYR13TFSI to the lithiumsalt was 20:100 in the preparation of the hybrid electrolytecomposition.

Example 3

A hybrid electrolyte composition was obtained in the same manner as inExample 1, except that the compound (D) obtained in Preparation Example2 was used instead of LiSTFSI in the preparation of the hybridelectrolyte composition. After polymerization as described below, apolymer of Formula 7 was obtained.

In Formula 7, n is 200.

Example 4

A hybrid electrolyte composition was obtained in the same manner as inExample 3, except that a mixing weight ratio of PYR13TFSI to the lithiumsalt was 20:100 in the preparation of the hybrid electrolytecomposition.

Comparative Example 1

N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide(PYR13TFSI) was used, as an ionic liquid.

Comparative Example 2

An electrolyte composition was obtained in the same manner as in Example1, except that 1-butyl-3-methyl-imidazolium tetrafluoroborate(imidazoliumBF₄) was used instead of PYR13TFSI, as an ionic liquid.

Comparative Example 3

An electrolyte composition was obtained in the same manner as inComparative Example 2, except that imidazoliumBF₄ as an ionic liquid,was not used.

Preparation of Cathode and Solid Secondary Battery Example 5

First, a cathode was prepared as follows:

LiCoO₂ (LCO), a conducting agent (Super-P; Timcal Ltd.), polyvinylidenefluoride (PVdF), and N-methylpyrrolidone were mixed to obtain acomposition for a cathode active material layer. A mixing weight ratioof the LCO, the conducting agent, and PVdF in the composition for acathode active material layer was 97:1.5:1.5, and an amount ofN-methylpyrrolidone was about 137 g when LCO was 97 g.

The composition for a cathode active material layer was coated on analuminum foil (thickness: about 15 μm) and dried at 25° C., and thedried resultant was dried in vacuum at about 110° C. to prepare acathode.

A lithium metal anode (thickness: about 20 μm) was disposed on a currentcollector (a copper foil), and the lithium metal anode and a solidelectrolyte were attached by applying a pressure of about 250 MPaaccording to a cold isostatic pressing (CIP) method. ALi_(6.5)La₃Zr_(1.5)Ta_(0.5)O₁₂ (LLZO) layer was used as an oxide-basedsolid electrolyte.

The cathode was impregnated with the hybrid electrolyte composition ofExample 1 and was attached on to the oxide-based solid electrolyte,i.e., LLZO layer, and the resultant stack was heat-treated at 60° C. toprepare a solid secondary battery including a cathode/oxide-based solidelectrolyte/lithium metal.

The cathode contained the hybrid electrolyte including a compound ofFormula 6, an ionic liquid, and a lithium salt on a surface of thecathode and in pores of the cathode.

In Formula 6, n is about 200.

A lithium metal is disposed such that it contacts a lower part of theLLZO layer.

Example 6

A solid secondary battery was prepared in the same manner as in Example5, except that the hybrid electrolyte composition of Example 2 was usedinstead of the hybrid electrolyte composition of Example 1.

Example 7

A solid secondary battery was prepared in the same manner as in Example5, except that the hybrid electrolyte composition of Example 3 was usedinstead of the hybrid electrolyte composition of Example 1. The cathodecontained the hybrid electrolyte including a compound of Formula 6, anionic liquid, and a lithium salt on a surface of the cathode and inpores of the cathode.

In Formula 7, n is 200.

Example 8

A solid secondary battery was prepared in the same manner as in Example5, except that the hybrid electrolyte composition of Example 4 was usedinstead of the hybrid electrolyte composition of Example 1.

Comparative Examples 4 to 6

Solid secondary batteries were prepared in the same manner as in Example5, except that the hybrid electrolyte compositions of ComparativeExamples 1 to 3 were each respectively used instead of the hybridelectrolyte composition of Example 1.

The solid secondary battery of Comparative Example 6 used the hybridelectrolyte composition of Comparative Example 3, not including an ionicliquid, and thus operation of the solid secondary battery of ComparativeExample 6 itself was impossible.

Evaluation Example 1: Viscosity

Viscosities of the hybrid electrolytes of Examples 1 to 3 and the ionicliquid of Comparative Example 1 were measured by using a viscometer(Brookfield]DV-II+PRO Viscometer) at 25° C., and the results are shownin Table 1.

TABLE 1 Sample Viscosity [cps] Comparative Example 1 573 Example 1 380Example 2 434 Example 3 420

As shown in Table 1, the viscosities of the hybrid electrolytes ofExamples 1 to 3 decreased compared to that of Comparative Example 1. Asthe hybrid electrolytes of Examples 1 to 3 had the viscosities shown inTable 1, the wettability with respect to a cathode was excellent.

In contrast, the ionic liquid of Comparative Example 1 exhibited anincreased viscosity compared to those of the hybrid electrolytes ofExamples 1 to 3, and due to the viscosity characteristic, thewettability with respect to a cathode was poor.

Evaluation Example 2: Electrochemical Stability

The hybrid electrolyte composition of Example 1 was coated on asubstrate, and the resultant was heat-treated at 60° C. for 2 hours toobtain a hybrid electrolyte.

The hybrid electrolyte was disposed between Li/Stainless steel (SUS)electrodes to prepare a cell. A linear sweep voltammetry (LSV) wasperformed on the cell at 60° C. to evaluate an electrochemical voltagewindow to evaluate electrochemical stability of the cell. The results ofthe LSV evaluation are shown in FIG. 2. A scanning rate was about 10millivolts per second (mV/s), and a scanning voltage range was about 3.2V to about 5 V (vs. Li/Li⁺). The results of the measurement are shown inFIG. 2.

As shown in FIG. 2, an oxidation reaction does not occur until 5 V, andthus the cell is electrochemically stable.

Evaluation Example 3: Resistance

An impedance analyzer (Solartron 1260A Impedance/Gain-Phase Analyzer)was used to measure resistances of the solid secondary batteriesprepared in Examples 5 to 7 and Comparative Examples 4 and 5 at 25° C.according to the 2-probe method. An amplitude was ±10 mV, and afrequency range was about 0.1 Hz to about 1 MHz.

The results of the resistance measurement are as shown in Table 2.

TABLE 2 Sample Resistance (Ω) Example 5 21 Example 6 59 Example 7 70Comparative Example 4 436 Comparative Example 5 89

As shown in Table 2, the interfacial resistances of the solid secondarybatteries of Examples 5 to 7 significantly decreased compared to thoseof the solid secondary batteries of Comparative Examples 4 and 5.

Evaluation Example 4: Lithium Ion Mobility

Lithium ion mobilities (t_(Li+)) of the hybrid electrolytes of Examples1 to 3 and the ionic liquid of Comparative Example 1 were evaluated asfollows.

The lithium ion mobilities may be calculated as defined in Equation 2.

As for values required for calculating the lithium ion mobility,impedance for a lithium symmetric cell or a SUS symmetric cell and acurrent decay decreasing by time with respect to an applied voltage weremeasured and used (Electrochimica Acta 93 (2013) 254).

$\begin{matrix}{t_{{Li}^{+}} = \frac{i_{ss}( {{\Delta V} - {i_{0}R^{0}}} )}{i_{0}( {{\Delta V} - {i_{ss}R^{ss}}} )}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

In Equation 2, i_(o) is an initial current, i_(ss) is a steady statecurrent, R⁰ is an initial resistance, and R_(ss) is a steady stateresistance.

The results of the lithium ion mobility evaluation are shown in Table 3.

TABLE 3 Sample Lithium ion mobility Example 1 0.52 Example 3 0.54Comparative Example 1 Lower than 0.20

Referring to Table 3, it may be seen that lithium ion mobilities of thehybrid electrolytes of Examples 1 and 3 increased compared to that ofthe ionic liquid of Comparative Example 1.

Evaluation Example 5: Charging/Discharging Cycle CharacteristicsAccording to Charging/Discharging Conditions

Charging/discharging characteristics of the solid secondary batteriesprepared in Examples 5 and 6 and Comparative Examples 4 and 5 wereevaluated by the following charging/discharging test.

The charging/discharging test was performed by placing the solidsecondary batteries in a constant-temperature chamber of 60° C.

In the first cycle, the batteries were charged with a constant currentof 0.3 milliamps per square centimeter (mA/cm²) for 12.5 hours until thebattery voltage was 4.3 volts (V). Subsequently, the batteries weredischarged with a constant current of 3.2 mA/cm² for 12.5 hours untilthe battery voltage was 3.0 V.

In the second cycle, the batteries were charged and discharged under thesame conditions of the first cycle. These cycles were repeated 50 timesunder the same conditions.

Changes in voltage according to a discharge capacity per unit area ofthe solid secondary batteries are shown in FIG. 3, and changes indischarge capacity according to the number of cycles are evaluated andshown in FIG. 4. Also, after the 50 cycles, contamination of the ionicliquid was examined.

Each sample underwent the cycles, and the pouch type cells weredisassembled. A lithium cobalt oxide (LCO) face of the solid electrolytecathode was examined, and the lithium anode face (a Li metal on thecopper foil) of the same solid electrolyte was examined. Particularly,in the case of the cell before applying solidification (ComparativeExample 5), it was observed that the ionic liquid penetrated into thecopper foil of the lithium anode face. Whereas, in the case of Example5, leakage of the ionic liquid of the electrolyte-solidification appliedcell was not confirmed.

Referring to FIG. 3, the solid secondary batteries of Example 5 and 6operated normally, and the cycle characteristics of the solid secondarybatteries of Example 5 and 6 improved compared to those of the solidsecondary batteries of Comparative Examples 4 and 5.

Referring to FIG. 4, the solid secondary battery of Example 5 hadimproved life characteristics compared to those of Comparative Example5.

Also, the ionic liquid of the solid secondary battery of ComparativeExample 5 leaked and thus the solid secondary battery was contaminated.In contrast, it is believed that the ionic liquid was not contaminatedin the lithium secondary battery of Example 5 because there was almostno leakage of the ionic liquid.

As described above, a cathode hybrid electrolyte for a solid secondarybattery according to an aspect of one or more embodiments is asolidified structure, of which contamination of a current collector andleakage to the outside of a current collector are prevented, and thewettability of the electrolyte to a cathode improves. Thus, interfacialperformance between the cathode and the solid electrolyte improves.Also, the cathode hybrid electrolyte has improved lithium ion mobility.When the cathode hybrid electrolyte of the current invention is used, asolid secondary battery having improved cycle characteristics and lifecharacteristics may be prepared.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments. While one or more embodiments have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope asdefined by the following claims.

What is claimed is:
 1. A cathode hybrid electrolyte for a solidsecondary battery, the cathode hybrid electrolyte comprising an ionconductor represented by Formula 1, and an ionic liquid, Formula 1

wherein, in Formula 1, X is an unsubstituted or substituted C6-C30arylene group, an unsubstituted or substituted C2-C30 heteroarylenegroup, or —C(═O)O—R₇—; R₇ is an unsubstituted or substituted C1-C30alkylene group or an unsubstituted or substituted C6-C30 arylene group;R₁ to R₃ are each independently hydrogen, an unsubstituted orsubstituted C1-C20 alkyl group, an unsubstituted or substituted C6-C20aryl group, or an unsubstituted or substituted C2-C30 heteroaryl group;—Y⁻ is an anionic moiety, wherein an anion of the ionic liquid comprisesthe same anionic moiety —Y⁻ as in Formula 1; and n is a degree ofpolymerization, which is a number in a range of 10 to
 500. 2. Thecathode hybrid electrolyte of claim 1, wherein —Y⁻ Li⁺ in Formula 1 is agroup represented by Formula 2 or Formula 3,

wherein, in Formula 2, Rf is a fluorine atom, an unsubstituted orsubstituted C1-C30 fluorinated alkyl group, an unsubstituted orsubstituted C6-C30 arylene group, or a combination thereof


3. The cathode hybrid electrolyte of claim 1, further comprising alithium salt different from the ion conductor of Formula
 1. 4. Thecathode hybrid electrolyte of claim 1, wherein the ion conductorrepresented by Formula 1 is a compound represented by Formula 4 or acompound represented by Formula 5,

wherein, in Formulae 4 and 5, n is a number in a range of 10 to 500, R₁to R₃ are each independently hydrogen or a C1-C20 alkyl group, and Rf isa fluorine atom, an unsubstituted or substituted C1-C30 fluorinatedalkyl group, an unsubstituted or substituted C6-C30 arylene group, or acombination thereof.
 5. The cathode hybrid electrolyte of claim 1,wherein the ion conductor represented by Formula 1 is a compoundrepresented by Formula 6, Formula 6-1, Formula 6-2, Formula 7, Formula7-1, or Formula 7-2, or a combination thereof,

wherein, in Formulae 6, 6-1, and 6-2, n is a number in a range of 10 to500,

and, in Formulae 7, 7-1, and 7-2, n is a number in a range of 10 to 500.6. The cathode hybrid electrolyte of claim 1 further comprising alithium salt different from the ion conductor of Formula 1, wherein anamount of the ion conductor is in a range of about 0.1 parts to about 50parts by weight based on 100 parts by weight of the lithium salt.
 7. Thecathode hybrid electrolyte of claim 1, further comprising a lithium saltdifferent from the ion conductor of Formula 1 wherein an amount of theionic liquid is in a range of about 1 part by weight to about 50 partsby weight based on 100 parts by weight of the lithium salt.
 8. Thecathode hybrid electrolyte of claim 1, wherein the ionic liquid is acompound represented by Formula 8, a compound represented by Formula 9,or a combination thereof,

wherein, in Formula 8, X₁ is —N(R₂)(R₃)(R₄) or —P(R₂)(R₃)(R₄), R₁, R₂,R₃, and R₄ are each independently an unsubstituted or substituted C1-C30alkyl group, an unsubstituted or substituted C1-C30 alkoxy group, anunsubstituted or substituted C6-C30 aryl group, an unsubstituted orsubstituted C6-C30 aryloxy group, an unsubstituted or substituted C2-C30heteroaryl group, an unsubstituted or substituted C2-C30 heteroaryloxygroup, an unsubstituted or substituted C4-C30 cycloalkyl group, anunsubstituted or substituted C3-C30 heterocycloalkyl group, or anunsubstituted or substituted C2-C100 alkylene oxide group,

wherein, in Formula 9,

is a heterocycloalkyl ring or a heteroaryl ring including 1 to 3heteroatoms and 2 to 30 carbon atoms, the rings substituted by asubstituent or unsubstituted, and X₂ is —N(R₅)(R₆), —N(R₅), —P(R₅), or—P(R₅)(R₆); wherein R₅ and Re are each independently hydrogen, anunsubstituted or substituted C1-C30 alkyl group, an unsubstituted orsubstituted C1-C30 alkoxy group, an unsubstituted or substituted C6-C30aryl group, an unsubstituted or substituted C6-CY30 aryloxy group, anunsubstituted or substituted C2-C30 heteroaryl group, an unsubstitutedor substituted C2-C30 heteroaryloxy group, an unsubstituted orsubstituted C4-C30 cycloalkyl group, an unsubstituted or substitutedC3-C30 heterocycloalkyl group, or an unsubstituted or substitutedC2-C100 alkylene oxide group; and Y⁻ is an anion, wherein at least aportion of the anions Y⁻ in Formulas 8 and 9 comprises the anionicmoiety —Y⁻ of Formula
 1. 9. The cathode hybrid electrolyte of claim 1,wherein the ionic liquid is a compound represented by Formula 10, acompound represented by Formula 11, or a combination thereof,

wherein, in Formula 10, Z is N or P; R₇, R₈, R₉, and R₁₀ are eachindependently an unsubstituted or substituted C1-C30 alkyl group, anunsubstituted or substituted C6-C30 aryl group, an unsubstituted orsubstituted C2-C30 heteroaryl group, an unsubstituted or substitutedC4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30heterocycloalkyl group, wherein, in Formula 11, Z is N or P; R₁₁, R₁₂,R₁₃, R₁₄, R₁₅, R₁₆, and R₁₇ are each independently hydrogen, anunsubstituted or substituted C1-C30 alkyl group, an unsubstituted orsubstituted C6-C30 aryl group, an unsubstituted or substituted C2-C30heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkylgroup, or an unsubstituted or substituted C3-C30 heterocycloalkyl group;and Y⁻ is an anion represented by Formula 2-1 or Formula 3-1,

wherein, in Formula 2-1, Rf is a fluorine atom, an unsubstituted orsubstituted C1-C30 fluorinated alkyl group, an unsubstituted orsubstituted C6-C30 arylene group, or a combination thereof


10. The cathode hybrid electrolyte of claim 1, wherein the ionic liquidis represented by one of Formulae 11a, 11b, and 12 to 15,

wherein, in Formulae 11a, 11b, and 12 to 15, R₁₈ to R₂₇ are eachindependently an unsubstituted or substituted C1-C30 alkyl group, anunsubstituted or substituted C6-C30 aryl group, an unsubstituted orsubstituted C2-C30 heteroaryl group, an unsubstituted or substitutedC4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30heterocycloalkyl group; and Y⁻ is an anion represented by Formula 2-1 orFormula 3-1,

wherein, in Formula 2-1, Rf is a fluorine atom, an unsubstituted orsubstituted C1-C30 fluorinated alkyl group, an unsubstituted orsubstituted C6-C30 arylene group, or a combination thereof


11. The cathode hybrid electrolyte of claim 1, wherein the ionic liquidis at least one of Formulae 30 to
 33.


12. The cathode hybrid electrolyte of claim 3, wherein the lithium saltcomprises at least one of LiPF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N,Li(CF₃SO₂)₃C, LiC₂FSO₃, Li(FSO₂)₂N, LiC₄F₉SO₃, LiN(SO₂CF₂CF₃)₂,LiN(CN)₂, or a compound represented by Formulae 16 to 19, and theconcentration of the lithium salt is in a range of about 0.01 moles perliter to about 5 moles per liter, based on a total volume of the hybridelectrolyte


13. The cathode hybrid electrolyte of claim 1, wherein the cathodehybrid electrolyte has an ion conductivity of about 0.5 Siemens percentimeter or higher and a lithium ion mobility of about 0.5 or greater.14. A cathode for a solid secondary battery, the cathode comprising: acathode active material; and the cathode hybrid electrolyte of claim 1.15. The cathode of claim 13, wherein the cathode comprises a pluralityof cathode active material particles, wherein the cathode hybridelectrolyte is disposed between the plurality of cathode active materialparticles, or the cathode comprises a cathode active material layercomprising the cathode active material, wherein the cathode hybridelectrolyte is disposed in at least one of pores in the cathode activematerial layer or on a surface of the cathode active material layer. 16.A solid secondary battery comprising: a cathode; an anode; and a solidelectrolyte disposed between the cathode and the anode, wherein at leastone of the cathode or the anode comprises the cathode hybrid electrolyteof claim
 1. 17. The solid secondary battery of claim 15, wherein thesolid electrolyte is an oxide-containing solid electrolyte.
 18. Thesolid secondary battery of claim 16, wherein the oxide-containing solidelectrolyte is at least one of Li_(1+x+y)Al_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂where 0<x<2 and 0≤y<3, BaTiO₃, Pb(Zr,Ti)O₃ (PZT),Pb_(1−x)La_(x)Zr_(1−y)Ti_(y)O₃ (PLZT) where 0≤x<1 and 0≤y<1,Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), HfO₂, SrTiO₃, SnO₂, CeO₂, Na₂O,MgO, NiO, CaO, BaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, TiO₂, SiO₂, SiC, lithiumphosphate (Li₃PO₄), Li_(x)Ti_(y)(PO₄)₃ where 0<x<2 and 0<y<3,Li_(x)Al_(y)Ti_(z)(PO₄)₃ where 0<x<2, 0<y<1, and 0<z<3,Li_(1+x+y)(Al_(a)Ga_(1−a))_(x)(Ti_(b)Ge_(1-b))_(2−x)Si_(y)P_(3−y)O₁₂where 0≤x≤1 0≤y≤1, 0≤a≤1, and 0≤b≤1, Li_(x)La_(y)TiO₃ where 0<x<2 and0<y<3, Li_(x)Ge_(y)P_(z)S_(w)) where 0<x<4, 0<y<1, 0<z<1, and 0<w<5,lithium nitride glass (Li_(x)N_(y)) where 0<x<4 and 0<y<2,SiS₂(Li_(x)Si_(y)S_(z)) where 0<x<3, 0<y<2, and 0<z<4, P₂S₅ glass(Li_(x)P_(y)S_(z)) where 0<x<3, 0<y<3, and 0<z<7, Li₂O, LiF, LiOH,Li₂CO₃, LiAlO₂, Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂-G_(e)O₂-type ceramics,garnet-type ceramics, Li_(3+x)La₃M₂O₁₂ where M=Te, Nb, or Zr, and x isan integer of 1 to 10, or a combination thereof.
 19. The solid secondarybattery of claim 16, wherein the cathode comprises a lithium nickelmanganese oxide compound, a lithium cobalt oxide compound, a lithiumnickel cobalt manganese oxide compound, a lithium nickel cobalt aluminumoxide compound, a lithium iron phosphate oxide compound, anoverlithiated layered oxide compound, or a combination thereof, andwherein the anode comprises amorphous carbon, crystalline carbon, ametal, a metalloid, or a combination thereof that forms an alloy or acompound with lithium as an anode active material.
 20. A method ofpreparing a cathode for a solid secondary battery, the methodcomprising: forming a cathode active material layer on a cathode currentcollector to prepare a cathode, the cathode active material layercomprising a cathode active material; providing a hybrid electrolytecomposition to the cathode, wherein the hybrid electrolyte compositioncomprises a monomer represented by Formula 20 and an ionic liquid; andapplying light or heat to the cathode to which the hybrid electrolytecomposition is provided to cause a polymerization reaction, to obtainthe cathode for a solid secondary battery comprising the cathode activematerial and the cathode hybrid electrolyte of claim 1,

wherein, in Formula 20, X is an unsubstituted or substituted C6-C30arylene group, an unsubstituted or substituted C2-C30 heteroarylenegroup, or —C(═O)O—R₇—; R₇ is an unsubstituted or substituted C1-C30alkylene group or an unsubstituted or substituted C6-C30 arylene group;R₁ to R₃ are each independently hydrogen, an unsubstituted orsubstituted C1-C20 alkyl group, an unsubstituted or substituted C6-C20aryl group, or an unsubstituted or substituted C2-C30 heteroaryl group;and —Y⁻ is an anionic moiety, and wherein an anion of the ionic liquidcomprises the same anionic moiety —Y⁻ as in Formula 20.